EP4583353A2 - Energiespeichersystem, ein-/aus-netz-schaltverfahren und leistungsumwandlungssystem - Google Patents

Energiespeichersystem, ein-/aus-netz-schaltverfahren und leistungsumwandlungssystem Download PDF

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Publication number
EP4583353A2
EP4583353A2 EP24221350.2A EP24221350A EP4583353A2 EP 4583353 A2 EP4583353 A2 EP 4583353A2 EP 24221350 A EP24221350 A EP 24221350A EP 4583353 A2 EP4583353 A2 EP 4583353A2
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EP
European Patent Office
Prior art keywords
power grid
angular frequency
pcss
pcs
grid
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Application number
EP24221350.2A
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English (en)
French (fr)
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EP4583353A3 (de
Inventor
Mingxuan Dong
Yunfeng Liu
Kai Xin
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Huawei Digital Power Technologies Co Ltd
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Huawei Digital Power Technologies Co Ltd
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Publication of EP4583353A2 publication Critical patent/EP4583353A2/de
Publication of EP4583353A3 publication Critical patent/EP4583353A3/de
Pending legal-status Critical Current

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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for AC mains or AC distribution networks
    • H02J3/28—Arrangements for balancing of the load in networks by storage of energy
    • H02J3/32—Arrangements for balancing of the load in networks by storage of energy using batteries or super capacitors with converting means
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for AC mains or AC distribution networks
    • H02J3/38—Arrangements for feeding a single network from two or more generators or sources in parallel; Arrangements for feeding already energised networks from additional generators or sources in parallel
    • H02J3/388—Arrangements for the handling of islanding, e.g. for disconnection or for avoiding the disconnection of power
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J7/00—Circuit arrangements for charging or discharging batteries or for supplying loads from batteries
    • H02J7/90—Regulation of charging or discharging current or voltage
    • H02J7/96—Regulation of charging or discharging current or voltage in response to battery voltage
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2207/00—Details of circuit arrangements for charging or discharging batteries or supplying loads from batteries
    • H02J2207/20—Charging or discharging characterised by the power electronics converter

Definitions

  • the energy storage system may participate in various adjustment tasks (such as reactive power adjustment) of the power grid through grid connection.
  • the energy storage system includes a plurality of power conversion systems (PCS, Power Conversion System), and output terminals of the plurality of PCSs are connected in parallel to connect to the power grid.
  • PCS power conversion systems
  • the PCS operates in a current source mode.
  • a characteristic of a current source is as follows: When on-grid, the PCS actively detects a frequency and a phase of a power grid voltage, and controls its own output current based on the frequency and the phase of the power grid voltage.
  • An internal impedance is characterized by a high value.
  • the energy storage system usually has a local load.
  • the PCS needs to be switched from an on-grid mode to an off-grid mode to supply power to the local load. This is referred to as on/off-grid switching of the PCS for short.
  • on/off-grid switching of the PCS for short.
  • the PCS needs to ensure as much as possible that a current provided to the load is not abruptly changed, so as to implement seamless on/off-grid switching
  • this application provides an energy storage system, an on/off-grid switching method, and a power conversion system, so that when PCSs perform on/off-grid switching, angles of output voltages of the PCSs are the same, thereby suppressing a relatively large cross current between the PCSs during on/off-grid switching, and supplying stable power to a local load.
  • An embodiment of this application provides an energy storage system, including a plurality of PCSs. Output terminals of the plurality of PCSs are connected in parallel to connect to an alternating current power grid. Input terminals of the plurality of PCSs are connected to an energy storage power supply. For example, there are at least two PCSs, and without communicating with each other, the at least two PCSs independently collect a power grid voltage at a parallel connection point, and independently implement on/off-grid switching. On/Off-grid switching principles of the PCSs are the same. To be specific, a first PCS of the at least two PCSs includes a voltage detection circuit, a power conversion circuit, and a controller. The first PCS is any one of the at least two PCSs.
  • the power conversion circuit converts, in an on-grid state, electric energy provided by the energy storage power supply, and outputs converted electric energy to the alternating current power grid.
  • the voltage detection circuit detects a power grid voltage at a parallel connection point of output terminals of the at least two PCSs.
  • the controller adjusts an angle of an output voltage of the first PCS to a reference angle. Because the reference angle is obtained by the first PCS based on an angular frequency of the power grid voltage when the at least two PCSs are on-grid, angles of output voltages of the at least two PCSs are the same.
  • the plurality of PCSs switch angles of output voltages to a same reference angle, so that phases of the output voltages are the same. Therefore, no large cross current is caused by a phase difference, that is, asynchronization, between the PCSs, and stable power can be supplied to a local load. It should be understood that, during on/off-grid switching, an angle of an output voltage of each PCS is synchronized with an angle of an output current, that is, the angle of the output voltage becomes consistent with the angle of the output current.
  • the output terminals of the plurality of PCSs are connected to the alternating current power grid, so that an angular frequency of a power grid voltage can be obtained in real time, and the reference angle can be obtained by using the angular frequency of the power grid voltage.
  • the plurality of PCSs need to operate off grid, that is, switch from on-grid to off-grid. This is simply referred to as on/off-grid switching.
  • Each PCS adjusts the angle of its own output voltage to the reference angle.
  • filtering may be first performed on an angular frequency, and a sum of an angular frequency obtained after the filtering and a reference angular frequency is then obtained; or a sum of an angular frequency and a reference angular frequency may be first obtained, and filtering is then performed on the sum.
  • the controller when each PCS is on-grid, performs coordinate transformation on the power grid voltage to obtain a Q-axis component in a rotating coordinate system, performs phase locking on the Q-axis component to obtain an angular frequency, performs low-pass filtering on a sum of the angular frequency and the reference angular frequency, and performs integration on an angular frequency obtained after the low-pass filtering to obtain the reference angle.
  • the controller performs coordinate transformation on the power grid voltage to obtain a Q-axis component in a rotating coordinate system, performs phase locking on the Q-axis component to obtain an angular frequency, performs low-pass filtering on the angular frequency, and performs integration on a sum of the reference angular frequency and an angular frequency obtained after the low-pass filtering to obtain the reference angle.
  • the controller is further configured to: obtain a phase of the power grid voltage when the at least two PCSs are on-grid, and correct the reference angle by using the phase of the power grid voltage; and when islanding occurs in the alternating current power grid, adjust the angle of the output voltage to a corrected reference angle.
  • the controller when the at least two PCSs are on-grid, the controller obtains the phase-locked angular frequency of the power grid voltage, and performs integration on a sum of the angular frequency and the reference angular frequency to obtain the phase of the power grid voltage.
  • the controller when the controller performs filtering on the sum of the angular frequency and the reference angular frequency, the angular frequency may be attenuated after the filtering, and an error may increase with time.
  • the reference angle obtained after the integration may also have an error. Therefore, the reference angle may be corrected at a scheduled time to compensate for the error of the reference angle. That is, the controller zeroes out the reference angle at a zero crossing point of the phase of the power grid voltage, and obtains the corrected reference angle by re-performing filtering and then integration on the phase-locked angular frequency of the power grid voltage.
  • the controller is further configured to: when the at least two PCSs are on-grid, use the phase of the power grid voltage as the angle of the output voltage of the first PCS.
  • a waveform of the reference angle is a sawtooth wave, and an angle of the sawtooth wave varies from 0 degrees to 360 degrees with a sine wave.
  • the controller detects a frequency or an amplitude of the power grid voltage at the parallel connection point, and when the frequency of the power grid voltage at the parallel connection point exceeds a preset frequency range or the amplitude of the power grid voltage at the parallel connection point exceeds a preset amplitude range, determines that islanding occurs in the alternating current power grid; and the controller is further configured to: when determining that islanding occurs in the alternating current power grid, set an islanding flag bit to 1, and set an angular frequency adjustment amount to 0, and is further configured to: when determining that a grid connection circuit breaker is disconnected, set the islanding flag bit to 2, and set the angular frequency adjustment amount based on a power angle characteristic, so that each PCS implements equal power division, where the grid connection circuit breaker is connected between the parallel connection point and the alternating current power grid.
  • an embodiment of this application further provides an on/off-grid switching method for an energy storage system.
  • the energy storage system includes at least two power conversion systems PCSs, output terminals of the at least two PCSs are connected in parallel to connect to an alternating current power grid, and input terminals of the at least two PCSs are connected to an energy storage power supply; and the method is applicable to a first PCS in the at least two PCSs, the first PCS is any one of the at least two PCSs, and the method includes the following steps: detecting a power grid voltage at a parallel connection point of the output terminals of the at least two PCSs; and when determining, based on the power grid voltage at the parallel connection point, that islanding occurs in the alternating current power grid, adjusting an angle of an output voltage of the first PCS to a reference angle, so that angles of output voltages of the at least two PCSs are the same, where the reference angle is obtained by the first PCS based on an angular frequency
  • the obtaining, when the at least two PCSs are on-grid, the reference angle by performing filtering and then integration on a phase-locked angular frequency of the power grid voltage specifically includes: when on-grid, performing coordinate transformation on the power grid voltage to obtain a Q-axis component in a rotating coordinate system, performing phase locking on the Q-axis component to obtain an angular frequency, performing low-pass filtering on a sum of the angular frequency and a reference angular frequency, and performing integration on an angular frequency obtained after the low-pass filtering to obtain the reference angle.
  • the obtaining, when the at least two PCSs are on-grid, the reference angle by performing filtering and then integration on a phase-locked angular frequency of the power grid voltage specifically includes: when on-grid, performing coordinate transformation on the power grid voltage to obtain a Q-axis component in a rotating coordinate system, performing phase locking on the Q-axis component to obtain an angular frequency, performing low-pass filtering on the angular frequency, and performing integration on a sum of a reference angular frequency and an angular frequency obtained after the low-pass filtering to obtain the reference angle.
  • the method further includes: obtaining a phase of the power grid voltage when the at least two PCSs are on-grid, and correcting the reference angle by using the phase of the power grid voltage; and when islanding occurs in the alternating current power grid, adjusting the angle of the output voltage to a corrected reference angle.
  • the obtaining a phase of the power grid voltage when the at least two PCSs are on-grid specifically includes: when the at least two PCSs are on-grid, obtaining the phase-locked angular frequency of the power grid voltage, and performing integration on a sum of the angular frequency and the reference angular frequency to obtain the phase of the power grid voltage.
  • the angular frequency adjustment amount is switched to 0, and in addition, the angle of the output voltage of each PCS is made consistent with the reference angle. After they are consistent, it is ensured that the angle of the output voltage of each PCS is the same, and then the angle is input to the PCS control loop for off-grid control.
  • the angular frequency adjustment amount is 0, and correction is performed on the reference angle by using a zero crossing point of a phase obtained after integration is performed on the reference angular frequency, so that the reference angle is zeroed out and corrected at the zero crossing point of the phase.
  • the angular frequency does not need to be adjusted, and the angular frequency adjustment amount output by the phase-locked loop PLL has no effect anymore. In this case, the angular frequency no longer changes.
  • a PPC in FIG. 1 is a power plant controller or a host computer.
  • the PPC is configured to control an open or closed status of the grid connection circuit breaker, for example, control the grid connection circuit breaker to be disconnected or connected.
  • the PPC controls the grid connection circuit breaker to be connected, and the PCS is connected to the alternating current power grid for on-grid operation.
  • Load is a local load.
  • the PPC controls the grid connection circuit breaker to be disconnected.
  • the PCS is disconnected from the alternating current power grid, operates off grid, and supplies power to the local load Load.
  • the PCS When the PCS operates on grid, the PCS operates in a current source mode. When the alternating current power grid fails and trips, the energy storage system needs to switch to operate off grid, to supply power to the local load. Therefore, the PCS needs to operate in a voltage source mode, to provide a stable voltage for the local load.
  • each PCS independently performs sampling, independently determines, based on a power grid voltage, whether islanding occurs, and performs off-grid control when islanding occurs. Because a cable length between a voltage detection circuit of each PCS and a parallel connection point varies, a line impedance varies with the cable length, and a generated voltage drop varies with the line impedance. Further, a power grid voltage detected by each PCS is different. As a result, an islanding moment of the power grid that is determined by each PCS is different. Further, a moment at which each PCS switches from on-grid to off-grid is different, and an output angle varies greatly. This causes a large cross current and affects stability of power supply to the local load.
  • the output terminals of the plurality of PCSs are connected to the alternating current power grid, so that an angular frequency of the power grid voltage can be obtained in real time, and a reference angle can be obtained by using the angular frequency of the power grid voltage.
  • the plurality of PCSs need to operate off grid, that is, switch from on-grid to off-grid. This is simply referred to as on/off-grid switching.
  • Each PCS adjusts an angle of its own output voltage to the reference angle.
  • FIG. 3 is a diagram of a control architecture of an energy storage system according to an embodiment of this application.
  • the energy storage system provided in this embodiment of this application includes at least two power conversion systems PCSs, and output terminals of the at least two PCSs are connected in parallel to connect to an alternating current power grid.
  • FIG. 3 only shows three PCSs schematically. A specific quantity of PCSs is not limited in this embodiment of this application.
  • Input terminals of the three PCSs are connected to an energy storage power supply.
  • the energy storage power supply may come from photovoltaic power, wind power, hydro power, or a battery. That is, the ESS outputs a direct current, and the PCS may convert the direct current into an alternating current same as that in the power grid.
  • An input terminal of each PCS may be connected to an independent ESS, or a plurality of PCSs may be connected to one same ESS.
  • the plurality of PCSs independently complete on/off-grid switching without being controlled by another device. Synchronization is not required between the plurality of PCSs, that is, the plurality of PCSs do not need to send an off-grid synchronization signal to each other.
  • each PCS independently completes its own on/off-grid switching. Therefore, for each PCS, an on/off-grid switching principle is the same.
  • any one of the plurality of PCSs is used as an example below for description, and another PCS has the same on/off-grid control principle. Details are not described herein.
  • a first PCS is used to represent any one of the plurality of PCSs.
  • the first PCS includes a voltage detection circuit 200, a power conversion circuit (that is, a PCS in the figure), and a controller 100.
  • the power conversion circuit is configured to: convert, in an on-grid state, electric energy provided by the energy storage power supply, and output converted electric energy to the alternating current power grid.
  • the voltage detection circuit 200 is configured to detect a power grid voltage at a parallel connection point of the output terminals of the at least two PCSs.
  • the parallel connection point is a point at which the output terminals of the plurality of PCSs are connected in parallel.
  • the output terminals of the PCSs are connected to a first side of a transformer, and a second side of the transformer is connected to the alternating current power grid.
  • the parallel connection point is a point at which the PCSs are connected to the first side of the transformer.
  • the controller 100 is configured to: when determining, based on the power grid voltage of the parallel connection point, that islanding occurs in the alternating current power grid, adjust an angle of an output voltage of the first PCS to a reference angle, so that angles of output voltages of the at least two PCSs are the same.
  • the reference angle is obtained based on an angular frequency of the power grid voltage when the at least two PCSs are on-grid. It should be understood that, because the reference angle is obtained when the plurality of PCSs are normally on-grid, reference angles obtained by the at least two PCSs are the same.
  • the PCS is required to supply power to the local load.
  • the PCS operates on grid, the PCS is equivalent to a current source, and the alternating current power grid provides a stable voltage for the local load.
  • the PCS operates off grid, the PCS needs to be equivalent to a voltage source to provide electric energy for the local load, so that the PCS provides a stable voltage for the local load.
  • a control loop in the figure is also implemented by the controller 100.
  • FIG. 3 shows a control link inside the controller 100.
  • a solid line in the controller 100 represents a working process in a normal on-grid case, and a dashed line represents a working process of the controller 100 in a case that islanding occurs in the alternating current power grid.
  • the voltage detection circuit 200 detects a three-phase voltage u abc at the output terminal of the PCS. Coordinate transformation is performed to transform a static coordinate system into a Q-axis component of the voltage in a two-phase rotating coordinate system. Then, the Q-axis component passes through a phase-locked loop PLL to obtain an angular frequency adjustment amount ⁇ pll representing a rotational speed of the power grid voltage.
  • the voltage in the rotating coordinate system is a vector, and the angular frequency is a frequency of rotation.
  • the angular frequency adjustment amount ⁇ ⁇ pll , that is, an angular frequency ⁇ pll output by the PLL and a reference angular frequency ⁇ B (a fixed angular frequency of the power grid is 50 Hz or 60 Hz) are added. Integration is performed on a sum of the angular frequency ⁇ pll and the reference angular frequency ⁇ B to obtain a phase ⁇ real of the power grid voltage.
  • 1 /s represents integration. In this case, the power grid is normal and no islanding occurs. Therefore, there is no islanding flag.
  • AI only indicates islanding detection.
  • AI1 is an output signal of AI, and is an islanding flag bit representing the islanding flag.
  • ⁇ pcs When AI1 is equal to 0, it indicates that the alternating current power grid is normal and no islanding occurs. This flag determines final ⁇ pcs for the control loop.
  • Islanding detection may be determined by using the power grid voltage, or may be determined by using a power grid current. For example, if an amplitude or a frequency of the power grid voltage has an offset, and is excessively large or excessively small, it may be determined that islanding occurs in the power grid. If the power grid voltage is normal, it is determined that no islanding occurs, and the PCS operates normally on grid. In this case, ⁇ pcs is equal to ⁇ real , that is, ⁇ real is directly output to the control loop.
  • the control loop herein refers to a control loop, for a power grid angle, that is required for the PCS to be on-grid, for example, a current loop, a voltage loop, or a power loop.
  • the control loop controls the PCS to perform power control or voltage control.
  • the foregoing control loops each are a control loop in a case that the PCS is normally on-grid. Details are not described herein. It should be understood that, the PCS works normally and performs voltage loop control, so as to detect its own output voltage.
  • the controller of each PCS obtains an angular frequency in real time by performing phase locking on the power grid voltage.
  • the reference angle is obtained based on the angular frequency.
  • the reference angle has no effect when no islanding occurs in the power grid, and plays a role only in an on/off-grid switching process.
  • a PLL of each PCS may output a different angular frequency adjustment amount. Consequently, an angle of an output voltage of each PCS is different, and there is a phase difference between the PCSs. This causes a relatively large cross current in an off-grid state.
  • the following describes a process, of switching from on-grid to off-grid, corresponding to the dashed line in FIG. 3 .
  • the controller When determining, based on the power grid voltage at the parallel connection point of the plurality of PCSs, that islanding occurs in the alternating current power grid, the controller adjusts the angle of the output voltage of the PCS to the reference angle.
  • ⁇ B is assigned to ⁇ real that is, ⁇ pcs used by the control loop at this time is equal to ⁇ B .
  • the reference angle ⁇ B is obtained by the at least two PCSs in the on-grid state based on the angular frequency of the power grid voltage. Reference angles obtained by the at least two PCSs are the same.
  • Each PCS independently implements on/off-grid switching.
  • each PCS obtains an angular frequency of the power grid voltage in real time, and obtains a reference angle based on the angular frequency of the power grid voltage. Therefore, the reference angle obtained by each PCS is the same.
  • each PCS switches to the respective obtained reference angle. Because the reference angle obtained by each PCS is the same, a large difference in the angles of the output voltages of the PCSs can be avoided, and a cross current between the PCSs can be further suppressed. It should be understood that, during on/off-grid switching, the angle of the output voltage of the PCS is the same as an angle of an output current, that is, the output voltage is synchronous with the output current.
  • the controller obtains the reference angle based on the angular frequency of the power grid voltage by filtering, for example, low-pass filtering or sliding average filtering.
  • filtering for example, low-pass filtering or sliding average filtering.
  • the PCS needs to provide the local load with a phase existing before the jump of the power grid voltage. Therefore, filtering is intended to make the angular frequency change slowly.
  • an input angular frequency encounters a transient change, an output angular frequency remains unchanged as far as possible. In this way, when the PCS is off-grid, an abrupt change of the angular frequency is turned into a slow change, thereby eliminating impact of a transient state.
  • filtering can also filter out an interfering signal.
  • a manner of obtaining the phase of the power grid voltage during normal on-grid operation is as follows: When the at least two PCSs are on-grid, the controller obtains a phase-locked angular frequency of the power grid voltage, and performs integration on a sum of the angular frequency and the reference angular frequency to obtain the phase of the power grid voltage, that is, ⁇ real .
  • each PCS implements operation in the off-grid state.
  • the energy storage system collects the voltage at the parallel connection point of the power conversion systems in real time.
  • the collected voltage signal passes through the phase-locked loop, to obtain the angular frequency adjustment amount.
  • An output angle is obtained by performing integration on the angular frequency obtained based on the sum of the angular frequency adjustment amount and the reference angular frequency, and the output angle is input to the PCS control loop for on-grid control.
  • filtering and integration are performed on the angular frequency, and then correction is performed to obtain the corrected reference angle. Because the plurality of PCSs have a same parallel connection point, a reference angle of each PCS is the same.
  • FIG. 8A is a diagram of yet another control architecture of an energy storage system according to an embodiment of this application.
  • three PCSs are still used as an example for description, which are respectively a PCS 1, a PCS 2, and a PCS 3.
  • An output terminal of the PCS 1 is connected to a first side of a first transformer T1
  • an output terminal of the PCS 2 is connected to a first side of a second transformer T2
  • an output terminal of the PCS 3 is connected to a first side of a third transformer T3.
  • a second side of T1, a second side of T2, and a second side of T3 are connected in parallel to connect to the alternating current power grid.
  • each PCS the output terminal of each PCS is not directly connected together, but is connected to an alternating current power grid through its own corresponding transformer. Therefore, a distance between each PCS and a parallel connection point may be different, a distance difference causes a different line impedance, and a generated voltage drop varies with the line impedance. Further, a power grid voltage detected by each PCS is different. As a result, an islanding moment of the power grid that is determined by each PCS is different. However, by using the technical solutions provided in the embodiments of this application, each PCS obtains a reference angle. When islanding occurs, an angle of an output voltage of the PCS is made consistent with the reference angle. Therefore, even if it is determined that an islanding moment is different, no relatively large difference exists between the angles of the output voltages. Therefore, there is no relatively large cross current between the PCSs.
  • an embodiment of this application further provides an on/off-grid switching method for an energy storage system.
  • the following describes the on/off-grid switching method in detail with reference to accompanying drawings.
  • FIG. 8 is a flowchart of an on/off-grid switching method for an energy storage system according to an embodiment of this application.
  • the on/off-grid switching method for an energy storage system is applied to an energy storage system.
  • the energy storage system includes at least two power conversion systems PCSs, output terminals of the at least two PCSs are connected in parallel to connect to an alternating current power grid, and input terminals of the at least two PCSs are connected to an energy storage power supply.
  • the method is applicable to a first PCS in the at least two PCSs, and the first PCS is any one of the at least two PCSs.
  • the method includes the following steps.
  • the method is applicable to any PCS, and a controller of each PCS performs the same method.
  • Each PCS may obtain the power grid voltage at the parallel connection point, to independently determine whether islanding occurs in the alternating current power grid.
  • the PCS is required to supply power to the local load.
  • the PCS operates on grid, the PCS is equivalent to a current source.
  • the PCS operates off grid, the PCS needs to be equivalent to a voltage source and provide electric energy for the local load.
  • a controller of each PCS obtains an angular frequency in real time by performing phase locking on the power grid voltage.
  • the reference angle is obtained based on the angular frequency.
  • the reference angle has no effect when no islanding occurs in the power grid, and plays a role only in an on/off-grid switching process.
  • each PCS when the power grid voltage is normal, each PCS operates normally on grid, and each PCS obtains the reference angle based on the angular frequency of the power grid voltage.
  • each PCS adjusts the angle of its own output voltage to the respective obtained reference angle. Because the reference angle obtained by each PCS is obtained by performing phase locking on the power grid voltage when the alternating current power grid is normal, the reference angle obtained by each PCS is the same.
  • each PCS switches the angle of the output voltage to the reference angle, that is, the angle of the output voltage is made consistent with the reference angle. This ensures that the angle of the output voltage of each PCS is the same, thereby suppressing a relatively large cross current between the PCSs, and ensuring that each PCS can supply stable power to the local load.
  • FIG. 9 is a flowchart of another on/off-grid switching method for an energy storage system according to an embodiment of this application.
  • filtering may alternatively be directly performed on the phase-locked angular frequency, summation is performed on an angular frequency obtained after the filtering and the reference angular frequency, and then integration is performed on an angular frequency obtained through the summation, to obtain the reference angle.
  • filtering may alternatively be directly performed on the phase-locked angular frequency, summation is performed on an angular frequency obtained after the filtering and the reference angular frequency, and then integration is performed on an angular frequency obtained through the summation, to obtain the reference angle.
  • FIG. 4A refer to the control architecture shown in FIG. 4A .
  • the angular frequency may be attenuated after the filtering, and an error may increase with time.
  • the reference angle obtained after the integration may also have an error. Therefore, the reference angle may be corrected at a scheduled time to compensate for the error of the reference angle.
  • the reference angle may be corrected by using the phase of the power grid voltage, and when islanding occurs in the alternating current power grid, an angle of an output voltage is adjusted to a corrected reference angle.
  • a specific correction process is as follows: The reference angle is zeroed out at a zero crossing point of the phase of the power grid voltage, and the corrected reference angle is obtained by re-performing filtering and then integration on the phase-locked angular frequency of the power grid voltage. The reference angle is zeroed out at each zero crossing point of the phase of the power grid voltage. Therefore, the reference angle is a periodic (0° to 360°) sawtooth wave, that is, an alternating current signal.
  • the angular frequency of the power grid voltage is specifically obtained as follows: Coordinate transformation is performed on the power grid voltage to obtain a Q-axis component in a rotating coordinate system, and phase locking is performed on the Q-axis component to obtain an angular frequency.
  • the filtering may be low-pass filtering or sliding average filtering.
  • each PCS switches an angle of its own output voltage to the reference angle, and performs on/off-grid switching.
  • an angular frequency adjustment amount is 0, and the reference angle is directly zeroed out and corrected at a zero crossing point of a phase obtained after integration is performed on the reference angular frequency.
  • the voltage at the parallel connection point of the power conversion systems is collected in real time.
  • the collected voltage signal passes through a phase-locked loop, to obtain the angular frequency adjustment amount.
  • An output angle is obtained by performing integration on the angular frequency obtained based on a sum of the angular frequency adjustment amount and the reference angular frequency, and the output angle is input to a PCS control loop for on-grid control.
  • filtering and integration are performed on the angular frequency, and then correction is performed to obtain the corrected reference angle. Because the plurality of PCSs have a same parallel connection point, a reference angle of each PCS is the same.
  • the angular frequency adjustment amount is switched to 0, and in addition, the angle of the output voltage of each PCS is made consistent with the reference angle. After they are consistent, it is ensured that the angle of the output voltage of each PCS is the same, and then the angle is input to the PCS control loop for off-grid control.
  • an embodiment of this application further provides a power conversion system PCS.
  • the power conversion system is disposed in an energy storage system, and the energy storage system includes a plurality of PCSs. Output terminals of the plurality of PCSs are connected in parallel to connect to an alternating current power grid.
  • the alternating current power grid is normal, the plurality of PCSs operates normally on grid.
  • the plurality of PCSs need to operate off grid to continue to supply power to a local load.
  • the PCS provided in this embodiment of this application is applicable to each PCS in the energy storage system.
  • the following describes the PCS from a perspective of one PCS, and an on/off-grid control process of each PCS is the same.
  • FIG. 10 is a schematic diagram of a power conversion system according to an embodiment of this application.
  • the power conversion system PCS provided in this embodiment of this application is a first PCS in at least two PCSs, the first PCS is any one of the at least two PCSs, and output terminals of the at least two PCSs are connected in parallel to connect to an alternating current power grid.
  • the first PCS includes a voltage detection circuit 101, a power conversion circuit 102, and a controller 103.
  • the power conversion circuit 102 is configured to: convert, in an on-grid state under control by the controller 103, electric energy provided by an energy storage power supply, and output converted electric energy to the alternating current power grid.
  • the voltage detection circuit 101 is configured to detect a power grid voltage at a parallel connection point of the output terminals of the at least two PCSs.
  • the controller 103 is configured to: when determining, based on the power grid voltage at the parallel connection point, that islanding occurs in the alternating current power grid, adjust an angle of an output voltage of the first PCS to a reference angle, so that angles of output voltages of the at least two PCSs are the same, where the reference angle is obtained by the first PCS based on an angular frequency of the power grid voltage when the at least two PCSs are on grid, and reference angles obtained by the at least two PCSs are the same.
  • the controller is specifically configured to: when the at least two PCSs are on-grid, obtain the phase-locked angular frequency of the power grid voltage, perform integration on the sum of the angular frequency and the reference angular frequency to obtain a phase of the power grid voltage, and correct the reference angle by using the phase of the power grid voltage; and when islanding occurs in the alternating current power grid, adjust the angle of the output voltage to a corrected reference angle.
  • Embodiment 9 The energy storage system according to any one of embodiment s 1 to 8, wherein a waveform of the reference angle is a sawtooth wave, and an angle of the sawtooth wave varies from 0 degrees to 360 degrees with a sine wave.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Supply And Distribution Of Alternating Current (AREA)
  • Inverter Devices (AREA)
EP24221350.2A 2021-07-30 2022-07-29 Energiespeichersystem, ein-/aus-netz-schaltverfahren und leistungsumwandlungssystem Pending EP4583353A3 (de)

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CN202110872541.3A CN115693731B (zh) 2021-07-30 2021-07-30 一种储能系统、并离网切换的方法及储能变流器
EP22187787.1A EP4125174B1 (de) 2021-07-30 2022-07-29 Energiespeichersystem und netzwerk/inselumschaltverfahren

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CN116345504A (zh) * 2023-03-28 2023-06-27 阳光电源（上海）有限公司 一种储能系统及电源系统
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US20230031139A1 (en) 2023-02-02
CN121923212A (zh) 2026-04-24
US12184073B2 (en) 2024-12-31
CN115693731A (zh) 2023-02-03
CN115693731B (zh) 2026-01-06
EP4583353A3 (de) 2025-09-17
EP4125174B1 (de) 2025-01-29
EP4125174A1 (de) 2023-02-01

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